This invention relates generally to a stereo/monaural selecting circuit which is operative to select automatically either a stereophonic operating state or a monaural operating state, and more particularly, is directed to a stereo/monaural selecting circuit for selectively rendering operative an amplifier section contained therein in either a stereophonic operating state or a monaural operating state in response to the existence or type of plug inserted into a jack provided.
Previously proposed compact stereophonic sound reproducing apparatus include a single speaker due to lack of enough space, and a sterephonic jack is provided. In the case where such a single speaker is utilized to reproduce sound, one channel signal of a stereophonic sound signal is supplied to the speaker to reproduce monaural sound. Stereophonic sound is reproduced by a stereophonic headphone having a binaural plug which is inserted into the stereophonic jack.
In the sound reproducing operation by the speaker mentioned above, there is the disadvantage that a listener hears an unnatural or strange sound even when the stereophonic sound signals in the left and right channels (L- and R-channels) represent ordinary stereophonic music, and further, the listener fails to hear some necessary information when the stereophonic sound signals in the L- and R-channels have different information from each other, because the sound which is heard is reproduced from only one of the stereophonic sound channel signals transmitted in the L- and R-channels, respectively. In order to avoid such disadvantage, it may be proposed to supply both of the stereophonic sound channel signals in the L- and R-channels to the speaker for reproducing sound by the speaker, and to supply separately each of the stereophonic sound signals in the L- and R-channels to the stereophonic headphone in the case of a sound reproducing operation by the stereophonic headphone. However, in this case, it is required that a first manual switch for selecting either the speaker or the stereophonic headphone and another second manual switch for selecting either the monaural operating state or the stereophonic operating state for the circuit be provided at the outside of the apparatus. This results in a relatively complicated construction and operation.
Further, a stereophonic sound reproducing apparatus is generally required to reproduce sound with not only a stereophonic headphone but also with a monaural earphone. For this purpose, a monaural jack is provided in the apparatus in addition to the stereophonic jack. This results in undesirable problems in space occupation in the apparatus and in usability of the apparatus. In addition, the sound reproducing operation by the monaural earphone has the same disadvantages as those inherent in the sound reproducing operation by the speaker, as aforementioned.
Such problems and disadvantages as mentioned above also occur with stereophonic sound recording apparatus. In the previously proposed stereophonic sound recording apparatus which is used with outer plugs supplying sound signals to be recorded, each of which may be attached to a microphone, a couple of independent jacks are provided further L- and R-recording channels, respectively, to receive the plugs, and in order to accomplish recording of the monaural sound signal, both sound signals supplied from the plugs to the L- and R-recording channels are mixed or one of these sound signals only is selected. Such stereophonic sound recording apparatus is complicated in circuit construction and difficult to control.